Changing feeding times/amount, help!

Some background info: I have four little ones, 3 girls and a boy. The boy is obese (about 20 lbs) and one of the girls is getting to be overweight (about 9-10lbs on a small frame). One of the other girls has had UTI issues for the past three weeks and my vet advised that if the antibiotics didn't cure it, I would likely have to change their diet, as I had been free feeding them nearly 100% dry food.
10 days of antibiotics later, Sofia started having the same UTI symptoms which appear to get better/stop when I feed her wet food only.
Since I have to change her entire food routine, I thought why not get everyone on a set schedule, stop free feeding, and hopefully help the two overweight cats get to a healthier weight.
The problem that I'm running into is that they are so used to having food available 24/7 that they only eat a little bit when I've put it out for them today at 9am,3pm, and 5pm. I eventually want to get them on a schedule of being fed once in the morning and once at night.
Does anyone have any tips on how to make the transition easier (on everyone!)? I don't want them to be hungry but I realize there is going to be a period of them getting used to the new routine.
Thanks in advance!

Piper, great work switching them all to canned! You should find that the heavy one loses weight, and it will especially help eliminate UTI's. I agree with Amber. They'll catch on quickly. The hungrier they are at set meal times the more they'll eat.

That is great that you are able to change their diet to wet food.=;
If you go to the site catinfo.org it will tell you how much to feed by how much your cat weighs, and will give you a formula to know how many calories to give. Dont go by what the can states as this is usually overstated. Also for your kitties that have the UTI's get as much water into them as possible. Proper nutrition can be a main preventative in many cats health problems. Also if you can find a wet food that is grain free, and has little to no fruits, vegies, and potato is preferable.

Hi Piper; congrats on switching to canned food!
I also bet that your cats will come around. I have 4 cats and always just left their morning canned food out until they got around to finishing it; in other words they had a long, lazy breakfast. But now, one of mine is on a rabbit only diet, so I can't leave the leftovers out. It took about a week, but the other 3 are getting the idea that they had better finish their food off when it's put out or they'll have to be hungry until the next meal time.
If none of your cats is on a special diet though, you can leave out their wet food until they finish it; you don't have to give them just 15 minutes for example. Leaving out their apportioned wet food is not the same as free feeding unless you think that your big guy will go and hoover up everyone else's leftovers.
Best of luck!
Shade